The present invention relates to a temperature control apparatus for vehicular catalytic converters, adapted to control the catalyst-bed temperature of the catalytic converters properly.
Exhaust gas from car engines contains noxious substances, such as CO, HC, NOx, etc., which will develop into air pollutants. Therefore, air pollution can be restrained by reducing production of these noxious substances or by purifying exhaust gas. To attain this, vehicles or cars are furnished with various means for reducing or purifying exhaust gas. Thus, the car engines are improved so that the production of the noxious substances are suppressed, and the exhaust gas from the engines is purified by removing the harmful substances therefrom by means of a catalytic converter. Conventional catalytic converters, used to purify the exhaust gas, include three-way catalytic converters, which serve to remove CO, HC, and NOx, and oxidizing catalytic converters which can remove CO and HC.
In general, a catalytic converter is mounted in an exhaust passage of an engine, and serves to purify exhaust gas of the engine discharged into the exhaust passage by removing the noxious substances from the gas. In this arrangement, the exhaust gas can be discharged into the atmosphere only after it is purified, thus making for the prevention of air pollution.
In view of warm-up performance, the catalytic converter should preferably be situated in a position near the engine where the temperature of the exhaust gas is high. For higher durability, on the other hand, it is advisable to locate the catalytic converter in a positions remote from the engine where the exhaust gas is at a relatively low temperature. With this arrangement, a rise of the converter temperature can be limited within an allowable range, so that the converter can be kept at a proper temperature. In other words, if it is situated close to the engine, the catalytic converter is liable to be heated. Although its warm-up performance is high, therefore, the converter tends to be heated to so high a temperature that it can be deteriorated quickly, and can therefore enjoy only a short life. If the converter is situated at a distance from the engine, on the other hand, its warm-up performance and hence purifying efficiency lower, although its life performance is improved.
Thus, the warm-up performance of the catalytic converter and the life performance or durability thereof are incompatible with each other.
In a temperature control apparatus disclosed in U.S. Pat. No. 3,851,469, a catalyst is prevented from being lowered in quality in the following manner. A catalytic converter is provided with a by-pass, which is adapted to open, thereby preventing exhaust gas from flowing into the converter, to restrain a rise of the catalyst temperature, when the temperature of the catalyst exceeds a set value. In this apparatus, all the exhaust gas is introduced into either the by-pass or the catalytic converter, in accordance with the catalyst temperature. Accordingly, it is difficult to keep the catalyst temperature constantly at a proper value. Thus, the required purifying efficiency cannot be obtained.